Geochronology,geochemistry and tectonic significance of the late Mesozoic volcanic sequences in the northern Wuyi Mountain volcanic belt of South China |
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| Institution: | 1. State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, China;2. State Key Laboratory of Geological Processes and Mineral Resources, Collaborative Innovation Center for Exploration of Strategic Mineral Resources, Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China;1. Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring, Ministry of Education, School of Geosciences and Info-Physics, Central South University, Changsha 410083, China;2. State Key Laboratory of Geological Processes and Mineral Resources, Collaborative Innovation Center for Exploration of Strategic Mineral Resources, Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China;3. State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, China;4. Institute of Isotope Hydrology, School of Earth Sciences and Engineering, Hohai University, Nanjing 210098, China;5. Shandong Bureau of China Metallurgical Geology Bureau, Jinan 250014, China;1. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029, China;2. University of Chinese Academy of Sciences, Beijing 100049, China |
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| Abstract: | The widespread occurrence of late Mesozoic volcanic rocks in the Gan-Hang Belt in South China is associated with similarly widespread mineralization, but many important questions surrounding these volcanic rocks have not been clearly answered. The Tianhuashan basin located in the northern Wuyi Mountain volcanic belt is one of the most important volcanic basins in the Gan-Hang Belt, and it is primarily composed of the Daguding and Ehuling Formations and their intrusive counterparts. LA-ICP-MS zircon U–Pb dating shows that the Daguding Formation erupted in the Late Jurassic (152–160 Ma), whereas the Ehuling Formation erupted in the Early Cretaceous (131–139 Ma) in the Tianhuashan basin. Volcanic rocks are rhyolite and share similar trace and rare earth element patterns with an enrichment of LREEs and a depletion in Sr, Ba, Nb, Ta, P, Eu and Ti. They are also characterized by negative whole rock εNd(t) and zircon εHf(t) values with Paleoproterozoic t2DM ages, suggesting that they were derived primarily from the remelting of ancient crustal materials. Daguding volcanic rocks are strongly peraluminous and show a higher Mg# than pure crustal melts, implying that they were likely derived from Paleoproterozoic metasedimentary basement materials. However, Ehuling volcanic rocks are weakly peraluminous and have a pronounced A2-type geochemical signature. Detailed elemental and isotopic data suggest that they were formed by the partial melting of the Paleoproterozoic metamorphic basement (including metasedimentary and metaigneous rocks) at a high temperature (~ 840 °C), followed by fractional crystallization. These results imply that during the Late Jurassic, South China on the Gan-Hang Belt was a continental arc coupled with the subduction of the Paleo-Pacific plate. Since the beginning of the Early Cretaceous, an intra-arc rift has formed along the Gan-Hang Belt as a consequence of slab rollback. These results also indicate that the extension in the Gan-Hang Belt began later than the southwestern part of the Shi-Hang Zone and lasted from 139 Ma to 122 Ma. |
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